MONDAY, Aug. 31, 2015 (HealthDay News) -- Teens with chronic diseases such as asthma and juvenile arthritis have to manage their health carefully, yet many of them have had alcohol or smoked marijuana in the last year, a new study shows.

"That was surprising to us," said study first author Elissa Weitzman, assistant professor of pediatrics at Boston Children's Hospital, about the findings. "We thought having a chronic illness might be protective, to some extent, given the potential for near-term serious health harm and the high value youth place on staying healthy."

But, she added, "While it's tempting to think that these youth are somehow immune from typical adolescent risk behaviors, they are not. They are exposed to marketing, promotion, peer behaviors, and like their peers, [they] are looking to have fun, fit in and 'escape.' "

The study was published online Aug. 31 in the journal Pediatrics.

For their analysis, Weitzman and her colleagues conducted a survey of just over 400 students. They were 9 to 18 years old, and the average age was about 15. All had a chronic disease, including asthma, cystic fibrosis, type 1 diabetes, juvenile arthritis, or inflammatory bowel disease. The participants completed the electronic survey during a visit to one of their specialist physicians.

A large portion of the children in the study, 75 percent, were white. Almost three quarters reported having a parent with a college degree.

Most of the children -- 82 percent -- were in high school. The researchers found that more than a third of the high school students with chronic disease had consumed alcohol in the past year. A fifth of the high schoolers had used marijuana in the last 12 months, the study found.

The teens who consumed alcohol were more likely than the nondrinkers to have missed or skipped taking their medications for their condition, the researchers said.

Alcohol has the potential to affect lab test results, and can interact negatively with medications, the researchers said. But nearly two-thirds of the children reported not knowing whether alcohol use can interfere with the effectiveness of lab test results. Almost half didn't know if alcohol could interfere with the effects of their medications.

"I think that the big take-home is if we can help educate them, we may be able to improve their compliance with their meds," said Dr. Ruchi Gupta, an associate professor of pediatrics at Northwestern University Feinberg School of Medicine in Chicago. "There needs to be an open, honest discussion about what they need to do to manage their disease, and the role that alcohol or marijuana or any substance can play in the effectiveness of their medication or how it's helping them," she added.

Weitzman echoed that advice. "We have found that youth really want to understand these risks and are looking for information to be delivered to them as part of their care," she said. "They are specifically interested in how alcohol and other substances can affect them and their disease."

The study authors wrote that these rates of alcohol and marijuana use are similar to those in the general population of healthy teens. One difference is that boys in the general population usually have a higher risk than girls for alcohol consumption, the study found. The new study found no effect of gender or ethnicity on the risk of alcohol or marijuana use.

When the authors looked at mental health status and substance use, they found that binge drinking was associated with a positive mental health status. That's possibly because students who binge drink are enjoying social time with peers, the researchers suggested.

In other words, chronic illnesses don't keep teens from acting like teens. "I think in general, in the populations of teens they're looking at, this is a huge time for risk-taking," said Gupta. "So this is a time when they are experimenting, thinking that they're indestructible."

Weitzman said the study authors also "are investigating whether this group of youth is also using substances to address symptoms of their conditions, side effects of their medications, or to 'treat' anxiety or depression, all factors that could play a role" in their behaviors. "Understanding these issues is vital to supporting these youth who face unique hurdles."